Electric discharge device



July 10, I934. FOUPKE 1,965,582

ELECTRIC DISCHARGE DEVICE Filed July 27, 1929 Patented July 10, 1934UNITED ST TES ELECTRIC DISCHARGE DEVICE Ted E. Foulke, Nutley, N. J.,assignor to General Electric Vapor Lamp Company, Hoboken, N. J., a.corporation of New Jersey Application July 27, 1929, Serial No. 381,424

3 Claims.

The present invention relates to electric discharge devices, and toelectrodes therefor. The particular object of the invention is toprovide a gaseous discharge device which will have i 5 a long-usefullife, will start upon the application of a relatively low potential,will operate at a correspondingly low voltage, and will maintain thesecharacteristics throughout its life. A further object of the inventionis to provide a method of producing such a. device. Other objects andadvantages of the invention will appear from the following particulardescription of a device embodying my invention and the method ofmanufacture thereof.

The invention consist of certain new and novel features of constructionand combinations of parts and also the new and novel steps in theprocessof manufacture of gaseous discharge devices, as hereinafter set forthand claimed.

Considerable difllculty has been encountered heretofore in theproduction of gaseous discharge devices which would function at normalcommercial potentials. It has been particularly desired to produce adevice of this character which 5 would consistently operate on 100-120volts D. C. Various expedients have been tried in order to accomplishthis, but these have resulted in short life of the device. By thepresent invention it has been found possible to produce a device whichwill start on the application of a direct current potential of the orderof 80 volts and which will have a useful life of several thousand hours.This has been accomplished by a modification of the activationheretofore used in devices of this type, as fully set forth in thefollowing specification.

For purposes of illustration a perspective view of an electric dischargedevice produced according to my invention is shown in the accompanyingdrawing.

In this drawing a sealed envelope 1 of glass, fused silica, or othersuitable material has sealed thereinto in a conventional manner theinleads 2 and 3 which respectively support the electrodes 4 and 5. Saidelectrodes have thereon a coating of material of low work function whichis produced in a manner which will be set forth in detail hereinafter.An insulating bead 6, in which terminate the ends of wires '7 which arewelded to the electrodes 4 and 5 near the upper edges thereof, serves tomaintain the proper spacing of said electrodes. The envelope 1 containsany suitable gaseous atmosphere, such as neon, helium, argon or mercuryvapor, or combinations thereof.-

A preferred method of preparing the device is as follows. The electrodes4 and 5 of iron or nickel are first carefully cleaned to remove anyforeign substances adhering thereto, after which they are raised to ahigh temperature either in a vacuum or, preferably, in an atmosphere ofhydrogen. In the latter case the electrodes become saturated withhydrogen to the exclusion of all other gases, and electrodes so treatedare found to be more easily freed of occluded gas in the later stages ofthe treatment. When cool the electrodes are coated with a compound ofpotassium, caesium, barium, strontium, or other alkali or alkaline earthmetal, or a combination thereof. This compound is preferably one, suchas the carbonate, which readily decomposes to the oxide when heated in avacuum. This material is conveniently applied to the electrodes 4 and 5by mixing it with a vehicle and either painting or spraying it thereon,or the electrodes may be dipped therein. It has been found that thepresence of suflicient carbon on the electrodes to reduce a portion ofthe alkaline oxide is desirable at a later stage. in the treatment,hence a vehicle such as collodion, the residue of which readilydecomposes to carbon when heated in a vacuum, is preferred althoughother vehicles such as alcohol or water may be used with good resutls.

The electrodes 4 and 5 are then sealed into the envelope 1 in the usualmanner, and the device placed in an oven and baked out at approximately450 C. for ten minutes, during which time-the envelope 1 is exhausted.By this treatment the envelope walls are made to give off any occludedgas and moisture. Then, the vacuum being maintained, the device isplaced within the influence of a high frequency magnetic field, theelectrodes 4 and 5 being heated thereby to a temperature ofapproximately 1000" C., driving all occluded gases out of saidelectrodes, reducing the carbonaceous vehicle to carbon, and reducingthe alkaline or alkaline earth compound to the oxide. A suitable gaseousatmosphere, such as a mixture of neon with about .5% argon, at apressure of about 5 m. m. of mercury is then admitted to the device.Then the electrodes 4 and 5 are again placed within a high frequencymagnetic field and raised to approximatelylOOO" C. Whileat thistemperature a high voltage discharge with a current density of the orderof .5 ampere per square inch of electrode surface is established betweensaid electrodes. As a result of the bombardment to which the electrodesare subjected by this discharge the surface of the alkaline or alkalineearth oxide is reduced 110 In the absence of carbon somewhat the sameresult seems to be obtained by mechanical absorption of the free oxygenatoms by the glass wall or other parts of the device, under the lowpressure of the gaseous atmosphere within the device. Due to the hightemperature of the electrodes during this bombardment there is a lowcathode drop so that there is little sputtering of the electrodematerial onto the walls of the envelope.

The gas mixture used during this treatment is then removed from thedevice, and the operating atmosphere admitted. The latter atmosphere maybe any of the usual vapors or monatomic gases, but is preferably amixture of either neon, or neon and helium, with from .1% to 5% ofargon, and is admitted at a pressure of the order of 15-25 m. m. ofmercury. The device is then sealed off, after which a high frequencydischarge of several amperes, or suflicient to raise the electrodes to ared heat, is maintained between the electrodes 4 and 5 until the surfaceof said electrodes is uniformly activated as evidenced by the uniformdistribution of the glow thereon. This will take on the order of 30seconds. The device is then burned on alternating current of commercialfrequency for several minutes, a discharge of the order of 100-200milliamperes per square inch of electrode surface being maintainedduring this period, the object of this treatment being to age theactivated surface in order to stabilize its operating characteristics.After this treatment a device so produced will have a breakdownpotential in the neighborhood of -100 volts D. 0.

Where the electrodes 4 and 5 are separated by a distance less than themeans free path of the ions of the gas utilized for the discharge, thedischarge is substantially confined to the outer faces ofsaidelectrodes. I have found that this same result may also be obtained,regardless of electrode separation, by coating only the outer face ofeach electrode with the alkaline compound, since the dischargemaintaining potential between the prepared surfaces is insuflicientthough the device is to be used on direct current,

since the device will then operate regardless of polarity, and byreversing the polarity after the coating on one electrode has'beenexhausted the coating on the other electrode can be utilized, therebyincreasing the useful life of the device.

The terms alkaline metal or alkaline oxide" as used in the claims areintended to cover metals of either the alkali or alkaline earth groups,or their oxides, respectively. v

It is 'to be understood that while the above process is preferred forthe production of my improved gaseous discharge device various changesmay be made in the process or in the separate steps thereof withoutmodifying or changing the essential features and characteristics of thedevice produced thereby, and that variations within the scope of theappended claims may be made in the device without departing from thespirit of my invention.

What is claimed is:

1. The method of producing electrodes for a gaseous discharge devicewhich comprises creating a coating of an alkaline oxide on saidelectrodes and then producing a layer of the alkaline metal on thesurface of saidoxide coating by bombarding said oxide with a highfrequency discharge while said electrode is maintained at a hightemperature.

' 2. The method of producing a gaseous discharge device which consistsin coating'the electrodes with an alkaline compound which is reducibleto the oxide, sealing said electrodes into an envelope, evacuating saidenvelope while heating said envelope and said electrodes to atemperature sufficient to drive off occluded gases, continuing to heatsaid electrodes in a vacuum to reduce said alkaline compound to theoxide, admitting a gaseous atmosphere to said envelope, raising saidelectrodes to a high temperature and producing a discharge therebetweento reduce the surface of said oxide to the metallic form, evacuatingsaid envelope, refilling said envelope with a desired gaseousatmosphere, and bombarding said electrodes with a high frequencydischarge.

3. The method of treating an electrode having a coating of an alkalineearth metal over a layer of the oxide of said metal which consists inbombarding said metal with a high frequency discharge to activate saidcoating and to reduce the work function thereof.

' TED E. FOULKE.

